Attempts will be made to isolate the isoenzymes of the catalytic subunit of the cyclic AMP-dependent protein kinase from gastric mucosa. If these enzymes are obtained in sufficient quantity, amino acid composition will be determined. The role of Mg ions in regulating the activity of this enzyme will be investigated. The cyclic nucleotide phosphodiestrases of the rabbit gastric mucosa will be characterized with respect to molecular weight, kinetics, and effects of potential effector molecules. Attempts will be made to isolate from the bullfrog gastric mucosa oxyntic cells that are responsive to secretagogues.